Apparatus for preparing paper pulp from used paper

ABSTRACT

The invention concerns a method and an equipment for combining in one single apparatus, the functions for filtering, decontaminating, and thickening paper pulp from used paper, while providing the complementary function of clarifying the filtrates. The apparatus ( 1 ) rotates at high speed. The paper pulp is introduced through the center of the apparatus ( 2 ) and driven at its angular speed. The pulp is then brought along a grate ( 6 ) with small size holes for separating the fibers from the greater part of the water. The thickened pulp is evacuated through extraction nozzles ( 8 ). The water is clarified in the clarification zone ( 12 ) and recycled or eliminated depending on uses. More complete embodiments of the apparatus include the functions of fractionating, de-inking and purifying the pulp with slots or holes.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/PT00/00006 which has an Internationalfiling date of Jun. 8, 2000, which designated the United States ofAmerica.

The present invention concerns the domain of the paper industry and morespecifically the preparation of pulp from recycling used papers toproduce paper.

For the manufacture of pulp from used paper, it is necessary to put thecellulose fibres in suspension and discard the undesirable foreigncomponents, called contaminants, being this operation calleddecontamination. The contaminants can have miscellaneous shapes. Inparticular, metallic particles (clips), sand and gravel, adhesivematerials, bits of plastic, . . . are found.

Inks are also found, which will be important to remove for someproductions, namely for papers called <<white>> aimed to be printed, tobe handwritten or for sanitary use (<<tissue>>).

In addition to the above-mentioned contaminants, mineral matter is alsofound, blended to the paper in some manufactures (magazines, paper forprinting, handwriting . . . ). The presence of mineral matter can beundesirable, in particular for the production of sanitary papers. Insuch cases their separation from the pulp is necessary.

The preparation of pulp using used paper is the global method, goingfrom disintegration of the used paper until the different stages ofdecontamination, eventually the elimination of inks (de-inking) and themineral matter (washing) and may include one or two whitening stagesallowing the fibres to recover their initial whiteness. The obtainedpulp will be used to feed the paper production apparatus.

The preparation of pulp for packing cardboards is much less demanding interms of decontamination.

The classic method of pulp preparation from used paper always beginswith the disintegration of the paper and the suspension of fibres, usinga pulping apparatus (Stage A). The pulping apparatus is an equipmentprovided with a rotor (or turbine), which causes a sufficiently strongstirring to the used paper, blended with water, that the connectionsbetween the fibres (hydrogen bonds) are broken one after another. Apaper pulp from used paper is thus obtained.

According to the quality of the final pulp to be obtained, the followingstages may be followed:

Stage B: A coarse decontamination. The coarser components and inparticular the plastic materials, are eliminated by passage through agrate.

Stage C: The elimination, by hydrocyclone, of the heavy coarse particleslike coarse sands, bits of glass, and metallic particles such as clips.

Stage D: The elimination of the small plastics and other contaminants ofintermediate size by the passage through a grate (or grate depuration)in two or three steps, consisting in passing the pulp through smallholes (between 1 and 3 mm) and retaining the contaminants of size higherthan the holes.

Stage E: The elimination of small contaminants, essentially of granularaspect (by opposition to plate contaminants) by a slot depuration(between 0.1 and 0.3 mm), working based in the same principle as thehole depuration. The holes are replaced by slots, which the fibres,taking into account their low diameter, are able to pass through.

Stage F: For the so-called <<white>> paper, the elimination of inks byone or several cells of flotation. Inks are separated with the help ofsmall air bubbles eventually with the help of a soap or a surfactant.

Stage G: The elimination of the fine sands and coarse black points(small heavy contaminants) by batteries of several stages ofhydrocyclones.

Stage H: In some cases, the elimination of small contaminants of densitylower than 1 by a hydrocyclone.

Stage I: More particularly applicable to tissue paper, the eliminationof the mineral matter by washing the pulp. The greater part of the wateris evacuated, taking with it the major part of the loads.

Stage J: Thickening of the pulp, to facilitate its storage beforereaching the paper apparatus or preparing the pulp by a hot dispersionor a refining.

Stage K: In some cases, dispersion of the residual contaminants, by onedispersant or grinder, in order to make these contaminants non visibleby the eye. In other cases, modification of the pulp mechanicalproperties by one refiner.

In many cases, redilution and repeating one or more of the previousdescribed stages is performed. It will then be called a second loop, oreven a third loop, if after the second loop one or several stages areagain repeated.

Stage L: Clarification of the filtrates by one microflotation deviceusing dissolved air. The suspended matter is collected in flocks andthen flotated at the surface with the help of air microbubbles andpolymers (flocculants and coagulants).

Stage M: Thickening of the solid matters extracted in Stage L.

Stage N: Treatment of the residual waters by a depuration station.

Stage O: Whitening of the fibres for certain uses.

The presently used methods of pulp preparation are a more or lesscomplete combination of the above-mentioned stages, each one performedby one different equipment. Between each stage, the pulp is generallypumped, causing a high energy consumption. Certain stages need the useof chemical products. It is frequent, particularly when the productionof <<white>> paper is wanted, to impose restrictive optical criteria,and then the method of recycling used paper is not competitive incomparison with the utilisation of virgin cellulose.

The invention has the object of replacing itself, in its base version,to several equipments corresponding to the above-mentioned Stages H, J,L, M, or even C, D, E, F, G and I, whatever may be the type of paper tobe produced, allowing also an important economy of energy and chemicalproducts. The recycling of the used paper will then be more competitive,including when aimed to more exigent applications. The invention alsoallows a very lower land investment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is represented by 6 drawings, corresponding to the mainuses and showing the main variants disclosed in the description. Theirnumbering corresponds to the references appearing in the text. Alldrawings are presented as merely indicative and without any limitativeintention.

FIGS. 1 to 4 represent several embodiments of the invention,corresponding to several uses. FIGS. 5 and 6 represent the details andspecific parts of the invention.

FIG. 1 represents a section of an embodiment of the invention moreparticularly applicable to sanitary papers (called <<tissue>>) in itsbase configuration having, besides the base functions, one device forthe recovery of the fibres having passed through the grate (6) and theirrecovery by the tube (14) at the centre of the device, one clarificationdevice in two stages, and one device for the reintegration of therecovered elements (13).

FIG. 2 represents a section of an embodiment of the invention moreparticularly applicable to sanitary papers having besides the basefunctions: one previous treatment of the pulp by elimination of the finesands and other <<heavy>> or <<light>> contaminants in the sedimentationchamber (25) and one classification by slots; one device for therecovery of fibres having passed through the grate (6) and theirconcentration in the chamber (33); one device for the reintegration ofthe recovered elements (13).

FIG. 3 represents a section of an embodiment of the invention moreparticularly applicable to printing and handwriting paper and paper fornewspapers and magazines, having, besides the base functions: oneprevious treatment of the pulp by elimination of the fine sands andother <<heavy>> or <<light>> contaminants in the sedimentation chamber(25) and one classification by slots; one pre-clarification device inthe chamber (33); one device for the reintegration of the recoveredelements (13).

FIG. 4 represents a section of an embodiment of the invention moreparticularly applicable to cardboard and packaging papers, having,besides the base functions: one previous treatment of the pulp byelimination of the fine sands and other <<heavy>> or <<light>>contaminants in the sedimentation chamber (25) and one classification byslots; one pre-clarification device in the chamber (33); one device forthe reintegration of the elements extracted during the clarification ofthe pulp by deflectors (39).

FIG. 5 represents a section of a classifier grate having holes/slots.

FIG. 6 corresponds to the speed-slowing device of the fibres extractedat the periphery (8) by tubes having the shape of a snail.

For sanitary papers, called <<tissue>>, the invention consists, in itsbase version, in regrouping the functions of washing, de-inking,elimination of the particles of density lower than 1, fibre thickening,thickening of the suspended matter from the filtered matter,clarification of water and elimination of contaminants having a densitylower than 1. The invention therefore replaces itself to the apparatuscorresponding to stages F, H, I, J, L, M of the classic method of paperpulp preparation. FIGS. 1 and 2 represent, in particular, twoembodiments of the invention applicable to this paper quality.

For printing and handwriting papers and papers for newspapers andmagazines, the present invention consists in regrouping, in its baseversion, the functions of de-inking, fibre thickening, clarification ofwater and elimination of the contaminants of density lower than to 1.The invention regroups stages F, H, J, L, M and eventually I of theclassic method of paper pulp preparation. FIG. 3 represents, inparticular, a embodiment of the invention for this application.

For the production of paper and packaging cardboard, utilising moreparticularly non-whitened fibres, the present invention consists inregrouping, in its base version, the functions of fibre thickening,clarification of water and elimination of contaminants with densitylower than 1, and eventually the fractioning of the long/short fibres.The invention replaces stages H, J, L, M of the classic method of paperpulp preparation. FIG. 4 is an embodiment of the invention for thisapplication.

In a more complete version for any applications, the invention replacesstages C to E and G of the classic method of paper pulp preparation.

The proposed apparatus comprises a body (1) rotating at a high speed anddriving with itself all internal constituents of the device. The body ofthe device is acted by one engine not represented in the figures.

In the past, used papers had to be disintegrated by means of a pulpier(Stage A), and be submitted to a coarse decontamination (Stage B). Inits base version (FIG. 1) the pulp should still be submitted to StagesC, D and E of the classical method before the introduction in theapparatus.

The pulp thus previously treated and free from the more importantcontaminants is introduced along the axis of the apparatus, by onecentral pipe (2). The blades (3) allow the pulp to be driven in rotationat the same angular speed as the apparatus. All inlet and outlet pipes(2), (12), (13), (14), (21), (22) and (37) are connected to mechanicaljoints, not represented in the figures, ensuring a sealed connexion withthe fixed pipes. The rotation speed of the device is such that theparticles are submitted at its periphery to an artificial gravity field,which may be higher than 1000 times the earth gravity.

In the base versions (FIG. 1), the pulp has already been submitted tostages A to E of the classical method and only contains smallcontaminants (having in general a diameter less than 0.5 mm). The pulpto be treated is taken (4) along a grate with small holes (6), themajority of water passing through the grate while the fibres areretained due to the low diameter of the holes. The fibres are driven,due to their density higher than 1, and under the effect of theartificial gravity field created by the apparatus rotation, to theapparatus periphery and lead the pulp into the concentration chamber(7). This action finishes at the extraction nozzles (8) with permanentor sequential aperture allowing the pulp to be extracted at an optimalconcentration.

In order to not damaging the fibres, the extraction being done at highspeed, the speed reduction of the pulp may be ensured by circular tubes(44) placed in a disposition having the shape of a snail (FIG. 6). Theextracted pulp at the periphery of the apparatus reaches thedeceleration rings whose dimensions are determined depending theacceptable maximum speed.

The contaminants of density lower than 1 not passing through the grate(6) migrate to the axis of the apparatus by the action of the artificialgravity field created by the apparatus rotation, where they arecollected and evacuated by a pipe (22).

The filtrates and water, having passed through the holes of the grate(6), are moved to the different treatments according to the uses.

For the version more particularly aimed to <<tissue>> uses (FIGS. 1 and2), one of the objectives of the invention is to recover the fibres andfines (fragments of fibres) having passed through the grate (6). The aimis also to eliminate ink and mineral matter from the water in order toreutilise it and to close at maximum the water circuits and to reducethe fresh water consumption. The non-clarified waters are, firstly,treated immediately their passage through the grate. The aim is torecover the fibres, which contain also the heavier and coarser elementsof the filtrates in question.

In order to recover the fibres having passed through the filtrationgrate (6), 2 different solutions are provided. The first solution,represented in FIG. 1, consists in leading the cellulosic elements to berecovered to the apparatus axis. The non-clarified water is conducted bythe pipe (9). The suction speed of the pipe (9) to the feed zone (15) ofthe clarification zone (16) is not sufficient to drive the fibres andother heavier particles, that therefore sediment at the periphery of thezone (5). These particles are recovered by a pipe (10) that take them tothe apparatus axis. The section of this pipe is designed to allow a flowspeed higher than the sedimentation speed of the fibres. At theperiphery of the chamber (5), an aperture (11) that communicates withthe concentration chamber (19) of the solid elements separated from thewaters to be clarified, allows to avoid the formation of sediments. Thisaperture may be passed by one counter-flow of water fed by a pipe (12).The flow rate of this water will be adapted so that the speed of theflow that passes through the aperture be higher than the fibresedimentation speed, while the high-density elements, that resist theflow due to their higher sedimentation speed, are collected in theconcentration chamber (19) before being extracted by the nozzles (20).The recovered fibres, collected by the pipes (10) and extracted by thecentre of the apparatus by the tube (14), are eventually treated byclassical means of de-inking before reintegrating the pulp in theapparatus.

The second solution for the separation of the fibres and their treatmentand recovery, consists in extracting them at the periphery of theapparatus. FIG. 2 is a representation of this configuration. The aim isto include a sedimentation zone (33) at the periphery of the zone (9)and downstream the grate (6) where the fibrous elements havingsedimented by the effect of the artificial gravity field, created by thefast rotation of the apparatus, are collected. These elements can thenbe evacuated at the periphery of the apparatus by the nozzles (34).Waters to be clarified go directly from the zone (33) to theclarification zone (16).

The fibres extracted by one of the two considered means are previouslytreated, if necessary, and may be reintegrated in the apparatus. Thisreintegration is performed by a pipe (13) that allows the leading of thefibres and other elements to be integrated to the apparatus periphery inthe points (13 b) of introduction in the zone (4). This localisation atthe periphery, next to the pulp concentration zone (7), allows limitingthe losses in fibres and other reintegrated elements, being the only aimto thick the pulp and reintegrated elements. The filtration grate (6)may have, for diameters higher than the point of reintroduction (13 b),holes of smaller size in order to limit the passage of the reintegratedelements through the grate.

For other applications (FIGS. 3 and 4), either for printing orhandwriting papers or packaging cardboards and papers, the watersseparated from the fibres are, for the greater part of these uses,directly connected to the clarification zone by the pipe (9). In effect,the greater part of the solid elements contained in the waters,including loads, and separated in the clarification stage, arereintegrated in the paper pulp after an eventual treatment. Thisreintegration can be performed according to a method identical to theabove-disclosed one.

For other applications, more particularly aimed to the production ofcertain packaging cardboards and papers needing specific mechanicalproperties, the grate (6) will also have a fractioning function, i.e.separation between long fibres and short fibres, the long fibres beingretained by the grate while the short fibres pass through it. In thisconfiguration, the size of the holes will be designed taking intoaccount the desired effect of fractioning.

For all applications, water and elements having passed through the grate(6) will be collected in the chamber (9) and taken to the clarificationzone (16) constituted by cones close to each other, made of plastic orcomposite matter with a density close to 1. Water to be treated,surrounded by the separation cones, is directed from the periphery tothe axis of the apparatus. The particles having a density different fromthat of water, under the effect of the artificial gravity field, have aradial speed different from the water one and find the surface of theclosest separation cone. Due to the friction between water and cones,the speed of water near the cones is very small, and this facilitatesthe migration of the particles along the conical surfaces. The particlescollected by the cones will have a migration speed higher than the waterspeed in the immediate vicinity of the cones. Once they meet one cone,the particles of density higher than 1 will then rise progressivelyalong the face of the cone. Water passes to the centre of the devicewhere it is evacuated by the tube (21).

The extremity at the periphery of each cone can be prolonged byevacuation channels (17) that allow the solids collected by the cones tocontinue their way to the periphery together with the non-clarifiedwater flow at the admission of the clarification. These channels,represented in FIG. 2, communicate themselves with the pipe for theevacuation of solids (18) before joining the concentration chamber (19)and being expelled from the apparatus by the nozzles (20). These nozzles(20) have an aperture permanent or sequential according to the case andthe uses.

A similar method will be utilised to separate and eliminate to the axisof the apparatus, by the action of the artificial gravity field, thecontaminants of density lower than 1 that migrate to the centre of theapparatus where they are collected by the pipe (37). In this case, thecones of the clarification zone (16) may be prolonged by the channels(36). This application is represented in FIG. 2.

In order to improve the quality of the water clarification and avoid asaturation of the circuits in mineral matter and other colloids linkedto an effect of clogging, particularly damaging to certain qualities ofpapers, the invention apparatus can be provided with a clarification in2 steps, where the water passes successively in a preclarification zone(33) and then in a final clarification zone (16), the two zones workingin series. In FIGS. 2, 3 and 4 this application is represented. Theobjective of the preclarification zone (33) is to eliminate the moreimportant particles, which in their displacement are susceptible tocreate a micro-turbulence that disturbs the sedimentation of the finerparticles. The zone of final clarification (16), with very close platesof separation, allows sedimentation of the finer elements according tothe principle already presented. Elements that are separated during thepreclarification by sedimentation in the chamber (33) are taken to theperiphery of the apparatus where they are evacuated at the periphery ofthe apparatus.

Another solution to obtain a preclarification and a final clarificationis the division of the clarification zone (16) in two sub-zones, bothequipped with separation cones, separated by an intermediate wall (35),that allows, once the preclarification is finished, to drive the waterto the final clarification. In FIG. 1 this solution is represented.

For some uses, and in particular those aimed to the production ofsanitary papers <<tissue>> (FIGS. 1 and 2), the solids that exit theclarification zone and are ejected by the nozzles (20) are not recoveredby the paper fabrication method, being the majority of the mineralmatter incompatible with the fabrication of <<tissue>> papers.

On the contrary, for the major part of the uses in papers for printingand handwriting, and papers/cardboards for packaging (FIGS. 3 and 4), atleast a part of these solids will be reintegrated in the pulp.

For use in paper for printing and handwriting (FIG. 3), the solidsextracted during the clarification will be extracted by the nozzles(20). It will be eventually needed to treat these particles to removeink and solids by conventional means (selective flotation) before,eventually, the reintegration by means of the above-mentioned pipe (13).

For some uses, the invention allows to reintegrate directly in the pulpall or part of the elements having been separated during theclarification step. FIG. 4 illustrates such use. Inclined deflectors(39) allow deriving a part of the elements having sedimented in thesedimentation chamber (33) to the pulp concentration chamber (7). Theaperture of these deflectors (39) may be fixed or adjustable in order toallow the mixture in the desired proportions of the fibres and thereintegrated elements, in particular the loads.

A more complete description of the invention, represented in FIGS. 2, 3and 4, will comprise the function described by Stage G, i.e. theelimination of fine sands as well as several contaminants. The pulp isintroduced in a chamber (25). The contaminants of density lower than 1are driven to the axis of the apparatus and are evacuated by openings(22 b) connected to the tube (22). The other solid elements, includingfibres, of density higher than 1, sediment at the periphery of theapparatus where they are collected by openings (26) located at theperiphery of the chamber (25) and taken by pipes (27) to the followingphase of the method. The pipe (27) is provided with openings allowingthe separation and the extraction of the contaminants of density higherthan 1 that have a speed of sedimentation higher than that of thefibres. These elements sediment and are separated by the openings (30)and extracted from the apparatus by the nozzles (38). The pipe (27) willhave an inclination and section adapted to avoid the sedimentation ofthe fibres and the passage of these ones in the openings (30). Toincrease the horizontal speed of the fibres and to limit the risk ofsedimentation, the pipe (27) will be fed by the water extracted in thecentral part of the chamber (25).

Whatever the uses may be, a more complete version of the inventionconsists in adding one classification by slots and/or holes. The aim isthen to perform Stages B to E of the classical method. Thisclassification is performed by a grate preferably with a conical shape(23). The grate (23) will be placed upstream of the grate (6) (FIGS. 2,3 and 4). The pulp is introduced at the axis of the device at theperiphery of the grate (23) according to a principle identical to thefiltration grate (6). The fibres pass through the slots (or holes),taking into account their small diameter, while some contaminants areretained.

The contaminants of high dimensions (which do not pass through thegrate) and have a density higher than 1 sediment and concentrate at theperiphery of the apparatus where they are extracted by severalextraction nozzles (38). The contaminants of density lower than 1 willmigrate to the axis of the device and will be extracted by a centralpipe (22). However, the presence of a separation chamber (25), upstream,comprising already a stage of elimination of the light contaminants maybe useless for many uses. The elimination of the light contaminants willbe made at the centre of the device. Counterwashing cycles, allowinglimiting the clogging of the grate, will be then sufficient to avoid thesedimentation of the lighter contaminants in the central part of theapparatus.

Water having passed through the slots (23), driving with it the fibresin suspension, is conducted to the axis of the apparatus by one pipe(24) to the zone (4), whose section is designed to impose a speedsufficient to the fluid to avoid a too fast sedimentation of the fibresto the periphery of the device.

In the case of using very contaminated used papers, it is possible toprovide a complementary removal of sands and the elimination of somecontaminants or inks having passed through the grate (23). In such aconfiguration, an aperture (not represented) at the part most inperiphery of the pipe (24) will allow the evacuation of the heavierelements by sedimentation. This aperture may be passed by onecounterflow of clear water whose flow rate would be adjusted so that thespeed of this counterflow be higher than the speed of sedimentation ofthe longer fibres and lower than the corresponding to the contaminantsto be separated.

In a more complete version, not represented in the figures, it will bepossible to add a grate provided with holes before the grate with slots(23), and working exactly according to the same principle. The holesallow a complementary decontamination helping the decontamination withslots. After finishing the stage of decontamination with holes, the pulpis introduced in the base of the grate with slots (23) according to theabove-described method.

It must be noted that the combined action of the foreseen separation inthe chamber (25) and of the grate with slots (23) will satisfy themajority of the uses by producing a pulp of quality sufficient for notneeding the passage through a grate with holes such as the one describedin the previous paragraph.

The grate with slots has the inconvenient of constituting a capacitylimitation of the apparatus. The open surface of the grate may be verysmall and not allow the passage of the permissible flow for all otherfunctions. To avoid this inconvenient, it is possible to create at theoutside of the grate one or several apertures (29) (represented in theFIGS. 2, 3 and 4) allowing to derive an important part of the flow tothe clarification zone. The peripheral disposition of these aperturesallows limiting the driving of the fibres, since these ones have alreadypassed through the slots (23). The contaminants being at the level ofthe aperture have a density higher than 1. The objective is to avoidthese contaminants to be driven before the water derived by theapertures (29).

To do this, the apertures will be disposed with a small retraction inrelation to the length walked by the contaminants on one hand, and willhave a funnel shape allowing the eventual contaminants closer to theaperture (29) to sediment at the periphery without being driven by theapertures (29). The derived water will be then directly conducted to theclarification zone. Any contaminant having, in spite of this, passedthese pipes will not cause any problem. It will be then possible, bymeans of addition of a water separation device, not represented in thefigures, to drive the derived water by the pipe (29) upstream thefiltration grate (6) in order to improve the washing effect.

The classifier grates (23) will have an adapted shape, in order toimprove their efficiency. The conical shape of the grate with slots orwith holes allows to easy the contact with the fibres and their passagethrough the grate. The angle of the cone will be designed to facilitatethe passage of the fibres. However, this conical shape has also as aconsequence the concentration of the contaminants of density higher than1 in the grate. In order to avoid the clogging of the holes, the grateis provided, for the majority of the uses with material relativelycontaminated, with angles <<ladder wise>> (28). FIGS. 2, 3 and 4represent such a grate (23) with the ladders (28).

The angle allows deviating the contaminants from the grate so that theygain speed before meeting again the grate. This device will facilitatethis way their sedimentation at the periphery of the grate. This anglewill facilitate, on the other hand, the passage of the fibres byregularly breaking the set of fibres that are formed at the surface ofthe grate.

The openings have a radial direction. The inlet of the openings isconical (40), and the cones of the adjacent openings will meet, in orderthat no plane surface between two cones exists. The objective is toconcentrate the fibres at the inlet of the openings, and to the directthem parallel to the openings, being the average length of the fibresmuch higher than the width of the openings. Once the minimum section isreached (41), the section of the openings raises (42) in order to avoidtheir clogging. FIG. 6 shows two openings in profile with thesedifferent dispositions.

What is claimed is:
 1. An apparatus for the preparation of paper pulpfrom used papers previously disintegrated and put in fibrous suspensionby a pulper, said apparatus comprising a body (1) rotating at high speeddriving together all components inside it, the body (1) comprising: aninlet pipe (2) for the fibrous suspension located at the centre of thebody (1), being the fibrous suspension driven at the angular speed ofthe body by means of blades (3) solidary with the body (1); a feedingzone (4) of a filtration grate (6) into which the fibrous suspensionintroduced in the body (1) of the apparatus is driven, being the grate(6) provided with small holes which allow to retain at least a part ofthe fibres contained in the suspension while the major part of thewater, small contaminants and mineral loads contained in the suspensionpass through the grate (6); a zone (7) for the concentration of the partof the suspension retained by the grate (6) located at the periphery ofthe feeding zone (4) of the grate (6); several apertures (8) located atthe periphery of the body (1) of the apparatus to evacuate theconcentrated suspension from the concentration zone (7); and aclarification chamber (16) to clarify the water having passed throughthe grate (6), the clarification chamber (16) comprising separationcones to facilitate the separation and migration of solid elementspresent in the water to be clarified, said clarification chamber alsoincluding apertures (20) located at the periphery of the apparatus body(1) for the evacuation of the solid elements having sedimented at theperiphery of said chamber (16) and a central pipe (21) for theevacuation of the clarified water; and a preclarification chamber (33),immediately upstream the clarification chamber (16), aimed to separatethe coarser solid elements before the final clarification of the water.2. An apparatus according to claim 1, characterized by the apparatuscomprising also one or several tubes (44) bent in a snail shape at theoutside of the body (1), whose inlets are located facing the apertures(8) for the evacuation of the concentrated suspension retained by thefiltration grate (6).
 3. An apparatus according to claim 1,characterized by the apparatus comprising also one central pipe (22)aimed to collect and evacuate from the apparatus body (1) the solidelements, present in the fibrous suspension and retained by thefiltration grate (6), which migrate to the centre the apparatus.
 4. Anapparatus according to claim 1, characterized by the separation cones ofthe clarification chamber (16) being prolonged in their peripheral partby channels (17) for the evacuation of separated particles having adensity higher than 1, these channels communicating with a pipe (18)ending in a concentration chamber (19), at the periphery of theclarification chamber (16).
 5. An apparatus according to claim 1,characterized by the separations cones of the clarification chamber (16)being prolonged in the direction of the apparatus axis by channels (36)for the evacuation of separated particles having a density lower than 1,these channels ending in a central pipe (37) for the evacuation of theseparated particles.
 6. An apparatus according to claim 1, characterizedby the clarification chamber (16) being divided in two chambersfunctioning in series, both equipped with cones and separated by acentral conical wall (35).
 7. An apparatus according to claim 1,characterized by the body (1) of the apparatus also comprising a devicefor the recovery of cellulosic particles having passed through thefiltration grate (6), said device being constituted by: a sedimentationchamber (5), immediately downstream the filtration grate (6) and at itsperiphery, where the major part of the heavy contaminants and cellulosicparticles having passed through the filtration grate (6) sediment, underthe effect of the artificial gravity field created by the rotation ofthe apparatus; a pipe (10), whose connection is located at the level ofthe sedimentation chamber (5) and which is oriented to the apparatusbody centre (1), collecting the particles and contaminants that havethere been sedimented, and dimensioned so that the flow speed in thispipe be higher than the speed of migration of the cellulosic particlesto the periphery, while the heavier contaminants sediment at theperiphery of said pipe (10); a central pipe (14) collecting, near theaxis of the apparatus, the flows of the pipe (10), mentioned at theprevious paragraph and allowing their evacuation from the apparatus body(1) by its axis.
 8. An apparatus according to claim 1, characterized bythe apparatus comprising an inlet pipe (13), which allows theintroduction into the fibrous suspension, at the inside of the apparatusbody (1), solid elements in points (13 b) located upstream thefiltration grate (6) and at the periphery of the feeding zone (4) ofsaid grate (6).
 9. An apparatus according to claim 8, characterized bythe filtration grate (6) being equipped with apertures of smallerdimension in the most peripheral part.
 10. An apparatus according toclaim 1, characterized by the body (1) of the apparatus comprisingapertures (34), at the periphery of the preclarification chamber (33),to evacuate from the apparatus body (1) the solid elements whichsediment at the periphery of said chamber (33).
 11. An apparatusaccording to claim 1, characterized by the body (1) of the apparatuscomprising inclined deflectors (39), fixed or adjustable, ensuring acommunication between the periphery of the preclarification chamber (33)and the concentration chamber (7) of the suspension portion retained bythe filtration grate (6).
 12. An apparatus for the preparation of paperpulp from used papers previously disintegrated and put in fibroussuspension by a pulper, said apparatus comprising a body (1) rotating athigh speed driving together all components inside it, the body (1)comprising: an inlet pipe (2) for the fibrous suspension located at thecentre of the body (1), being the fibrous suspension driven at theangular speed of the body by means of blades (3) solidary with the body(1); a feeding zone (4) of a filtration grate (6) into which the fibroussuspension introduced in the body (1) of the apparatus is driven, beingthe grate (6) provided with small holes which allow to retain at least apart of the fibres contained in the suspension while the major part ofthe water, small contaminants and mineral loads contained in thesuspension pass through the grate (6); a zone (7) for the concentrationof the part of the suspension retained by the grate (6) located at theperiphery of the feeding zone (4) of the grate (6); several apertures(8) located at the periphery of the body (1) of the apparatus toevacuate the concentrated suspension from the concentration zone (7);and a clarification chamber (16) to clarify the water having passedthrough the grate (6), the clarification chamber (16) includingapertures (20) located at the periphery of the apparatus body (1) forthe evacuation of the solid elements having sedimented at the peripheryof said chamber (16) and a central pipe (21) for the evacuation of theclarified water; and a sedimentation device upstream the filtrationgrate (6), in order to make a separation of some contaminants with bigdimensions contained in the fibrous suspension introduced in theapparatus, said device being constituted by: a sedimentation chamber(25); a hole (22 b) located in the part closer to the axis of thesedimentation chamber (25), aimed to separate the light elements whichthere concentrate and driving them to the central pipe (22) and allowingtheir elimination; a hole (26) located at the periphery of thesedimentation chamber (25), aimed to separate the heavy elements,including cellulose fibres, which there sediment; a pipe (27) derivingthe part of the fibrous suspension having passed into the chamber (25)and having not been separated by the holes (22 b) and (26) of separationof light and heavy elements, into the feeding zone (4) of the filtrationgrate (6), or to the following stage of the method, if a complementarydevice is located between the sedimentation device and the filtrationgrate feeding zone; said pipe (27) having an inclination and sectionadapted so that the cellulosic elements are driven by the flow withoutsedimenting there; a pipe connecting the hole (26) for the separation ofheavy elements to the pipe mentioned in the previous paragraph; a hole(30) for the elimination of heavy elements, in the peripheral part ofthe pipe (27) mentioned at paragraph d), aimed to collect and separatethe heavier contaminants which sediment at the periphery of said pipe(27); and a pipe leading the solid elements captured by hole (30) forthe elimination of the heavy elements mentioned at paragraph f) to theapertures (38), located at the periphery of the body (1), for theevacuation of the elements collected by said hole (30).
 13. An apparatusfor the preparation of paper pulp from used papers previouslydisintegrated and put in fibrous suspension by a pulper, said apparatuscomprising a body (1) rotating at high speed driving together allcomponents inside it, the body (1) comprising: an inlet pipe (2) for thefibrous suspension located at the centre of the body (1), being thefibrous suspension driven at the angular speed of the body by means ofblades (3) solidary with the body (1); a feeding zone (4) of afiltration grate (6) into which the fibrous suspension introduced in thebody (1) of the apparatus is driven, being the grate (6) provided withsmall holes which allow to retain at least a part of the fibrescontained in the suspension while the major part of the water, smallcontaminants and mineral loads contained in the suspension pass throughthe grate (6); a zone (7) for the concentration of the part of thesuspension retained by the grate (6) located at the periphery of thefeeding zone (4) of the grate (6); several apertures (8) located at theperiphery of the body (1) of the apparatus to evacuate the concentratedsuspension from the concentration zone (7); and a clarification chamber(16) to clarify the water having passed through the grate (6), theclarification chamber (16) including apertures (20) located at theperiphery of the apparatus body (1) for the evacuation of the solidelements having sedimented at the periphery of said chamber (16) and acentral pipe (21) for the evacuation of the clarified water; and aclassifier device upstream the filtration grate (6), aimed to separatethe contaminants having a dimension higher than the cellulose fibres,said apparatus being constituted by: a classifier grate (23) having aflat or conical shape and having calibrated slots or holes such that themajority of the cellulose fibres pass through the slots and/or holes;apertures (38) located at the periphery of the apparatus body (1) andupstream the classifier grate (23), allowing to evacuate the elements,which do not pass through the slots and/or holes and migrate to theperiphery of said grate (23); a central pipe (22) aimed to collect andevacuate from the apparatus body (1) the elements, which do not passthrough the slots and/or holes, and migrate to the axis of theapparatus; and a pipe (24) leading the water and the elements havingpassed the classifier grate (23) to the feeding zone (4) of thefiltration grate (6).
 14. An apparatus according to claim 13,characterized by the apparatus body (1) comprising a device for thederivation of a part of the water, upstream the classifier grate (23),said apparatus being constituted by: a water inlet (29) having a conicalshape and oriented perpendicularly to the trajectories of the particles,located at the periphery and upstream the classifier grate (23); and apipe connecting the water inlet mentioned at the previous paragraph andthe clarification chamber or the feeding zone (4) of the filtrationgrate (6), according to the uses.
 15. An apparatus according to claim13, characterized by the classifier grate (23) being conical andincluding one or several inclinations (28) in order to avoid theaccumulation of solid elements along the classifier grate (23).
 16. Anapparatus according to claim 13, characterized by the holes (40) of theclassifier grate (23) having a radial direction and an entrance with theshape of a funnel, the entrances with the funnel shape of two adjacentholes joining themselves at the side upstream the grate in order toavoid any plane surface between two holes, and this being done tofacilitate the orientation and the passage of the fibres.
 17. Anapparatus according to claim 13, characterized by the holes (40) of theclassifier grate (23) being comprised by an inlet funnel and an outletfunnel in order to facilitate the passage of the fibres and avoid therisk of clogging.
 18. An apparatus according to claim 1, characterizedby the holes of the filtration grate (6) being calibrated to allow thepassage of an important part of the short cellulose fibres and retainthe majority of the long cellulose fibres, performing therefore afractioning between short fibres and long fibres.
 19. An apparatusaccording to claim 1, characterized by the apparatus comprising acentral pipe aimed to lead directly to the inside of the apparatus body(1), at the level of the clarification chamber, some non-thickenedsemi-liquid effluents such as the foams of a de-inking cell.